Incandescent lamp.



G. M. J. MACKAY.

INCANDESCENT LAMP.

APPLICATION F|LED SEPT. 11. 19:4.

L1 9 Patented Oct. 26, 1915.

Fig.1.

Inventor: George T-flimackag,

enonen M. J. or, or sonnn'fscranx, NEW YORK, Assrenon r0 GENERAL nnncrnrc COMPANY, A CORPORATION or new roan INCANDESGENT LAMP.

Mamas.

Specification of Letters Patent.

Patented Uet. 26,1915.

. a neationmea September 11, 191a. Serial No. 861,279.

To all whom it may concern: 7

Be it known that I, GEORGE M. J. MAGKAY, a subject of the King of Great Britain, residing at Schenectady county of Schenectady, State of New Yor have invented certain new and useful Improvements in Incandescent Lamps, of which the following is a specification.

The {present invention comprises an incandescent lamp having a concentrated light source and particularly useful in focusing devices, such as projectors.

In a lamp embodying my invention the incandescing glower comprises a filament made to, assume a compact form by disposing one closely coiled part inside. another.

It is one of the features of my invention to proportion the filament to operate at substantially the same temperature throughout.

The accompanying drawings show in Figure 1 in perspective one form of a completed lamp embodying my invention and Fig. 2 is an enlarged detail view of a double helix filament.

My invention is applicable to evacuated as well as gasfilled lamps, but it is of particular utility in the gasfilled type of lamp' because of the decreased cooling effect of the tit gas convection currents on an incandescent body crowded into a relatively small space.

Fig. 1 shows in general outlines a lamp having a concentrated light source and particularly suitable for projector purposes, as in automobiles, motor boats, stereopticons, and the like. The filament or glower 1 comprises two helices connected in series as more clearly shown in Fig. 2. Although I prefer to use a filament of tungsten my invention, of course, isapplicable to glowers of other refractory materials, The leads 2, 3 are sealed into a stem 4 of the globe 5 in the usual manner and suitably connected tothe lamp base 6. The globe 5 is either evacuated or filled with nitrogen, argon, or other gas inert with respect to the filament, or mixtures of these gases. The gas pressure preferably approximates atmospheric pressure at the operating temperature of the lamp. In a gas filled lamp the filament 1 may be operated at a higher temperature than in a vacuum, preferably at a temperature giving a specific consumption of about one-half watts per candle power or even lower.

Unless special'provision is made the inner helix Wlll operate at a higher temperature than the outer due to the fact that it is closely surrounded by the. outer helix, receives heat therefrom and cannot lose as much heat by radiation. The turns of the 1n ner spiral should be spaced closely to, each other so as to conserve ,loss of heat by conduction through the gas, but the turns of the outer surrounding helix should be spaced far enough to allow the light from the inner helix to be emitted and will be cooled to a greater extent than the inner helix. To compensate for this inequality in the rate of heat loss of the two helices, the helices are constructed to generate heat at unequal rates, for example, the outer helix is made of correspondingly higher resistance per unit length than the inner helix. As, shown in Fig. 2 the outer helix '1 has a smaller diameter than the inner helix 8. For example, a lamp consuming 4.5 amperes at 8 volts may have a filament in which the diameter of the wire constituting the outer helix is about 7 mils and the wire constituting the inner helix is about 8 mils. A greater amount of heat is generated in the outer turns and thus compensates for the greater rate of heat dissipation and causes'the filament to operate at a substantially uniform temperature. No fixed rule for proportioning the resistance of the helices can be given as the heat losses depend on many factors. The terminal wires 9 and-10 are preferably but not necessarily notched or reduced in diameter near the helices to reduce the heat losses bv conduction.

What I claim as new and desire to secure by Letters Patent of the United States, is:

1. An incandescent lamp comprising an incandescent filament part of which is surrounded bv' another part, said inclosed and inclosing parts being proportioned to operate at substantially the same temperature.

2. An incandescent electric lamp, comprising an envelop, and a coiled conductor of refractory material therein, comp-risingsections located one within the other, the inner section having a lesser resistance per unit length than the outer section.

3. An incandescent electric lamp comprising an envelop, a filling of inert gas -at relatively considerable pressure therein,

in the other, the filament section consti-- tuting the inner helix having a greater cross-section than the outer.

4. A concentrated source incandescent lamp, comprising an envelop, a filling of inert gas therein, and a tungsten filament mounted therein comprising at least two sections connected in series, one of said sections being surrounded at least in part by another section, the outermost section having a greater resistance per unit length than the inner section or sections.

5. An incandescent lamp comprising an rality of turns, one part of said filament turns inclosing another part, said filament being constructed to operate at a substantially uniform temperature.

In- Witness whereof, I have hereunto set 20 my hand this 8th day of September, 1914.

GEORGE M. J. MACKAY.

Witnesses:

HELEN Onronn, BENJ. H. Wmsrmon. 

